Aluminum is conventionally produced by reduction of alumina dissolved in a molten cryolite bath within an electrolytic reduction cell.
In the Soderberg electrolytic cell, the anode of the cell is maintained by adding a carbonaceous anode paste to the upper surface of the anode. The lower surface of the anode is consumed in the electrolytic process. Thus, at regular intervals, the anode is lowered and the anode paste applied, such that the size of the anode is maintained between acceptable upper and lower limits.
As the anode is lowered, the anode paste is baked into a hardened state, such that when it reaches the position in the anode where it is to be the current conducting portion of the anode, i.e., near the bottom of the anode, it is fully baked.
Electrical current is supplied to the anode through a plurality of anode pins which are located across opposing surfaces of the anode. Once the anode is fully baked, it is extremely difficult, if not impossible, to drive anode pins into it. Thus, it is common practice to insert anode pins into the anode at a substantial distance above the position where these pins are used.
The pins are located across the face of the anode by means of a channel having a plurality of openings therein through which the pins are inserted into a desired position.
With the need for the pins to be inserted into the anode substantially above the vertical position where they are employed, a typical Soderberg anode has, at any given point in time, multiple levels of anode pins and channels vertically "stacked" above one another, with the lowermost set of anode pins at any given time being electrically connected and conducting current through the anode.
As previously mentioned, the anode pins are inserted through openings located in the channels which position the pins both horizontally and vertically. Traditionally, anode channels included a plurality of generally horizontal openings such that the anode pins in a given layer are in a generally horizontal line. Unfortunately, however, this location of the anode pins does not place the majority of the pins in the most ideal location for even current distribution through the anode. During the baking of the anode in operation of the cell, the outer edges of the anode are baked somewhat slower than the center of the anode due to air cooling of the edges of the anode. Thus, the uneven baking causes an uneven current distribution in the cell when electrical current is applied horizontally across the anode. It would be desirable, therefore, to provide for a more even current distribution in the anode by locating the anode pins across the surface of the anode in a way more closely corresponding to the current distribution in the anode.